Compression fittings for the manufacture of a permanent, tight connection between tubes. The fitting has at least one end, which has a hook-shaped cross section and a bead-like configuration, which end holds an O-ring and can be compressed with the tube. An adjacent cylindrical section extending in the longitudinal direction, which is provided at the end with a bead-shaped recess acting as a stop for the flat-ended tube which can be inserted.

To create a compressible fitting that can be economically manufactured and still provide rapid connection technology, the invention proposes that the area characterizing the type of fitting is designed as a cast or molded basic body fabricated from a metal or non-metal material, that is connected to a standardized connection piece made of sheet metal, whereby this connection piece has a bead-like end holding an O-ring and an adjacent cylindrical area, which is provided at the end with a bead-like recess acting as a stop for the flat-ended tube which can be inserted.

Compression fittings made of carbon steel or high-alloy steel, for interior installation, are known in the prior art. A brochure published by Mannesmann Edelstahlrohr GmbH shows such a fitting. The core of this system is a deformable compression fitting fabricated from a section of tube which, depending on whether it is designed as an elbow, tee or reducer, has at least one end that is hook-shaped and bead-like and holds a gasket. Adjacent to this end is a cylindrical area extending in the longitudinal direction. Attached to the end of the extension of this cylindrical area is a bead-shaped recess which extends radially inward and serves as a stop for the flat-ended tube that can be inserted. By means of an activation apparatus that is connected with a locating device having hinged jaws, the bead-like end is plastically deformed and the enclosed gasket is elastically deformed.

In addition, with the same compression process in the cylindrical area of the fitting, in the immediate vicinity of the bead-like end, a bead-shaped recess is pressed and the tube inserted underneath it is compressed along with it. The elastically deformed gasket in this connection system performs the sealing function, while the compressed bead-shaped recess absorbs the longitudinal forces produced by the internal pressure.

A disadvantage of this system is that on account of the high requirements regarding surface quality and dimensional tolerances, the compression fitting is fabricated from a section of a specially manufactured tube, using several deformation and transformation steps. The basic, or initial, tube is usually a seamless or longitudinally-welded tube that is subjected to a heat treatment following cold deformation. This specially manufactured tube requires close tolerances and a high surface quality. To manufacture a compression fitting from this tube, the original tube is cut into sections and the desired final cross section shape is produced by performing several transformation steps, e.g. tapering, crimping and chasing. Since the basic product, or raw material, is already relatively expensive, the compression fitting manufactured from it is also relatively expensive.

The advantage of the proposed compression fittings is that the region defining the type of fitting, e.g. elbow, tee or reducing connector, is cast or molded from a metal or non-metal material and the basic body fabricated in this manner is permanently connected to a standardized connection piece. With an eye toward achieving the most economical solution possible, the invention also proposes that the basic body be made of simple or higher-grade gray cast iron. It is also possible to use a compressible plastic with or without reinforcing fiber filler for the manufacture of the basic body.

The standardized connection piece, like the compression fitting of the prior art, has a bead-like end holding an O-ring and an adjacent cylindrical section which, at the end, has a bead-shaped recess (i.e. a reduction of the unobstructed inside diameter) that acts as a stop for the flat-end tube that can be inserted. The connection between the basic body and the connection piece, depending on the material pair in question, is made by soldering or welding, or using adhesives, so that the hole in the connection piece, or fitting, makes a smooth transition into the hole in the basic body. This prevents the occurrence of unacceptably high flow losses on account of eddy formations, or turbulence, at the connection point.

Some examples of compression fittings can be found in U.S. Pat. No. 4,891,877, entitled "Portable Tool for Compressing a Fitting on a Hose; and U.S. Pat. No. 4,567,841, entitled "Fairing Assembly for Towed Underwater Cables.